1. Field of the Invention
This invention relates to a novel electrode material for a non-aqueous liquid electrolyte secondary cell employing the electrode material.
2. Description of the Related Art
In keeping up with recent progress in electronics technology, portable electronic equipments, such as a video tape recorder with a built-in camera, a portable telephone or a lap top computer, have been developed, and hence a strong demand has been raised towards development of a small-sized lightweight secondary cell of high energy density as a portable power source for using these equipments.
As a secondary cell, satisfying this demand, a non-aqueous liquid electrolyte secondary cell of high energy density employing light metals, such as lithium, sodium or aluminum, as active materials for negative electrode, and which is capable of developing a theoretical high voltage, is promising. In particular, the non-aqueous liquid electrolyte lithium secondary cell is easy to handle and capable of achieving a high output and a high energy density, so that researches and development in this field are proceeding briskly.
Meanwhile, if light metal, such as lithium metal, is directly used as a negative material for the non-aqueous liquid electrolyte secondary cell, the light metal tends to be precipitated as dendrites on the negative electrode in the course of charging, so that the current density is increased significantly at the distal end of the dendrite. The result is that the cyclic durability tends to be lowered due to decomposition of the non-aqueous liquid electrolyte or the dendrite is grown excessively to produce internal shorting in the cell.
For preventing such dendritic precipitation of light metals, these light metals are not used directly, but are used as doping materials for a carbonaceous material capable of doping and undoping ions of light metals so as to be used as a negative material. As the carbonaceous materials, cokes or organic high-molecular sintered materials are used in view of production cost and cyclic characteristics.
The energy density of the secondary cell having such negative electrode depends appreciably on the amount of doping/undoping of light metal ions in the carbonaceous material, that is charging/discharging capacity.
However, the amount of doping/undoping light metal ions in a conventional carbonaceous material cannot be said to be sufficient, and hence development of a novel negative electrode material having a higher charging/discharging capacity has been desired.
The carbonaceous material, such as cokes or organic high-molecular materials, are produced using fossil resources, such as cal or petroleum. From the viewpoint of maintaining or improving earth environments, use of such materials is not wholly desirable, such that a novel negative electrode material to take the place of the carbonaceous material has strongly been desired.